INVESTIGADORES
VILANOVA Isabel
congresos y reuniones científicas
Título:
Vegetation and climate change during the last glacial termination in the modern forest-steppe ecotone, central Patagonia (~46°S)
Autor/es:
ISABEL VILANOVA; RODRIGO VILLA-MARTINEZ; PATRICIO MORENO
Lugar:
Salvador
Reunión:
Congreso; XIV International Palynological Congress X International Organisation of Palaeobotany Conference; 2016
Institución organizadora:
IFPS ? International Federation of Palynological Societies, IOS ? International Organisation of Palaeobotany and ALPP ? Asociación Latinoamericana de Palaeobotánica y Palinología.
Resumen:
Little is known about the vegetation that developed along the eastern margin of the Patagonian Ice Sheet (PIS) during the last glacial termination (termination 1 = T1, ~11-18 ka, ka= 1000 cal yr BP) in central Patagonia (45°- 48°S), as well as the local timing, structure and rates of climate changes over this transition, arguably the largest and fastest of all climate changes on Earth during the Cenozoic. The southern westerly winds (SWW) constitute the sole source of precipitation to the central Patagonian Andes, where a formidable west to-east decline in precipitation drives a strong zonation of vegetation units ranging from North Patagonian rainforests in the pacific coast to the Patagonian Steppe in the extra Andean plains to the east. Here we present a pollen record from Lago Unco (45°34´29.4´´S; 71°43?7.6´´W, 756 masl), a small closed-basin lake located in the modern forest-steppe ecotone indirect association with moraines deposited by the Coyhaique/Balmaceda piedmont glacier lobe during the youngest advance of the last glacial maximum (LGM). The record starts with very low pollen concentrations between 16.5-17.7 ka consisting of herbs and shrubs characteristic of cold high-Andean environments and the Patagonian steppe (Poaceae, Asteraceae subfamily Asteroidae, Ericaceae and Apiaceae). A sustained rise in Nothofagus ensued (11-16.5 ka), accompanied by the hygrophilous cold-resistant conifer Fitzroya/Pilgerodendron, the herb Gunnera, the pteridophytes Blechnum and Lycopodium magellanicum, along with traces of the tree Drimys winteri. Because these moisture-dependent taxa are absent in the Patagonian Steppe, we interpret colder and hyperhumid conditions relative to the present along the eastern Andean slopes during T1, implying stronger-than-present SWW influence. The presence of cold-resistant hygrophilous taxa so early during T1 (the earliest in any published record in the region) suggests that these taxa thrived near the eastern margin of the PIS during the LGM and may have been a source for the postglacial dispersal and colonization of trees currently dominant in rainforests along the pacific coast of central Patagonia. We observe the appearance (14.5 ka) and subsequent increase (11.5-12.8 ka) of the conifer Podocarpus nubigenaat times of maximum abundanceof Nothofagus (~45%) attesting for the proximity of humid forests. The slight increase of littoral macrophytes  Cyperaceae) between 11.3-10.9 ka reflect alower water level of Lago Unco probably due to warm/dry conditions linked to lower SWW intensity. We will compare these results with palynological data from contemporary sites (Lago Edita, L. Churrasco, L. Mellizas) located ~20 km upwind.